Since the development of the first fluid containing system, system designers have faced the need of preventing unauthorized access to such systems. While systems that are formed of entirely permanent fittings would be most highly tamper resistant and tamper obvious, the necessity of providing ingress and egress ports in most fluid systems has created the need for security caps to protect such ports.
Tampering with such systems may come in many forms, ranging from attempted access by well meaning but unauthorized persons to outright vandalism. Systems that are exposed to public access are the most vulnerable, while systems containing potentially harmful substances are the most important to protect. Examples would include drains of various types, particularly those draining chemical or plating tanks or otherwise providing access to hazardous substances; service access ports to various refrigeration systems, and access to such non-hazardous but critical systems as pneumatic tires.
Additionally, the public is exposed to many systems that operate under high pressures wherein an unsuspecting party tampering with the system may be seriously injured, if not killed, by a high pressure fluid escaping the fluid handling system. Such systems may include by way of example, and not limitation, gas, hydronic, steam, refrigerant, and compressed air piping systems, as well as many others.
A particular need for such a security cap exists in the refrigeration and air conditioning fields. Current environmental and safety standards have mandated a high degree and care in the handling of refrigerants. For example, Section 608 of the Federal Clean Air Act requires that all persons who maintain, service, repair, or dispose of appliances that contain regulated refrigerants be certified in proper refrigerant handling techniques. Obviously, the intent of this federal law is negated if equipment design allows unauthorized or untrained persons easy access to such refrigerants.
In attempts to discourage unauthorized access to fluid systems, various designs of security cap devices have been proposed. In general, such devices rely on one of two general mechanisms, the use of a non-standard fitting and tool for removal, or the shrouding of the cap within a protective device.
In the first group, typical of those methods utilizing non-standard tools for security caps, is U.S. Pat. No. 5,033,501 to Stehling, which provides a non-standard tool for the removal of fire hydrant caps. In a similar vein, U.S. Pat. No. 3,935,877 to Francheschi provides for a non-standard wrench to operate the water valve of a fire hydrant. The use of non-standard tools to prevent fitting removal is not restricted to cap or valve embodiments, however, as seen in U.S. Pat. No. 4,018,111 to Goldhaber and U.S. Pat. No. 6,024,522 to Bainbridge, et al., both of which provide security fasteners that are difficult to remove without a specially adapted tool.
The particular weakness of these non-standard tool based designs is that it is frequently possible to grip the non-standard fitting with a gripping tool, such as vise grip pliers or a pipe wrench, and thereby use a compression grip on the non-standard fitting to remove it. Some devices, such as the '501 device, attempt to use a grip resistant profile to discourage such tampering, but as long as any edges or irregularities are accessible, it is possible to defeat these caps with a suitable gripping tool.
A second group of designs that attempt to prevent unauthorized access rely on shrouding the fastener or access cap with some type of shrouding device. One type of design utilizes a locking shroud that completely covers the access area, as seen in U.S. Pat. No. 5,996,613 to Bertolotti. Such locking designs require a relatively complex and cumbersome lock and key assembly, and are not well suited for small embodiments. Another design is that of capped shrouds; such as seen in U.S. Pat. No. 5,791,371 to Kemp, or U.S. Pat. No. 5,890,859 to Hasnik; which rely on a non-standard tool to remove the cover of a capped shroud that covers a standard fitting. These shrouds also have significant drawbacks. The '371 device may be easily defeated by the use of snap ring or needle nose pliers in the keyholes of the locking cap, and additionally has a large sidewall on the cap that could easily be grasped with a gripping tool described above. The '859 device has an extremely small pin that is difficult to manipulate even for authorized access to the fastener.
A proposed solution has been to combine non-standard caps and shrouds in an attempt to have the two mechanisms cancel each others weaknesses. An example is seen in U.S. Pat. No. 3,453,655 to Quinones, et al., which employs a non-standard fitting recessed with a fixed shroud to operate the valve of a fire hydrant. The weakness of such a device is that the non-standard fitting is not a cap, but is an integral part of the valve itself. Therefore, such a system cannot be retrofitted onto a standard threaded cap installation by simply replacing the cap with a security cap. A rotating shroud is seen in U.S. Pat. No. 6,062,787 to Maddalena, wherein an outer shroud may rotate around an inner cap. However, like the '371 device above, simple tools, or even a piece of bent wire, may be used to defeat the keyhole security system and remove the shroud. Furthermore, the close tolerance between the outer shroud and the inner cap in the '787 device makes it likely that a compressing tool may be used to crush the shroud against the cap in order to effectuate its removal.
Accordingly, the art has needed a means of preventing access to fasteners or fluid system ports that is simple, lightweight, inexpensive to fabricate, and easily retrofitted onto existing applications, that at the same time is exceedingly difficult for unauthorized parties to access.